1. Field of the Invention
This invention relates to the preparation of catalysts, and more particularly to a method of preparing a supported gold catalyst for carbon monoxide oxidation by using an ion exchange scheme.
2. Description of the Prior Art
The use of catalysts for low-temperature carbon monoxide (CO) oxidation is of importance in environmental protection, industrial processes, and some instruments. In the past, gold (Au) has been less frequently considered as a catalyst material due to its chemical inertness. An upsurge of interest in gold as a catalyst material was aroused by the work of Haruta et al., i.e. Japanese Patent JP 60 238,148 entitled "Gold-based oxide catalyst for catalytic combustion of fuel gases". They reported that Au/Fe.sub.2 O.sub.3, Au/Co.sub.3 O.sub.4 and Au/NiO, which were prepared by a coprecipitation method, were effective in promoting the oxidation of carbon monoxide even at a temperature as low as -70.degree. C. By such a coprecipitation method, the surface areas of catalysts were low and the gold loadings were usually larger than 10 wt. %. As a result, significant amount of gold probably was buried inside the host metal oxide particles and could not be used for CO oxidation. Furthermore, these gold-host oxide catalysts prepared by precipitation method should be supported on appropriate carriers before being practically used. Therefore, an improvement by supporting gold and iron oxide on various carriers has been reported by Haruta et al., i.e. Japanese Patent JP 01 94,945 entitled "Catalysts from gold ultrafine particle-loaded metal oxide fixed on supports and manufacture thereof". However, there is an ever present need to develop new, water-durable and effective CO oxidation catalyst compositions and/or improved processes for preparing effective CO oxidation catalyst compositions.